On Thu, Jun 02, 2016 at 03:29:18PM +0900, Joonsoo Kim wrote: > On Thu, Jun 02, 2016 at 01:29:16PM +0900, Minchan Kim wrote: > > On Thu, Jun 02, 2016 at 11:22:43AM +0900, Joonsoo Kim wrote: > > > On Thu, Jun 02, 2016 at 09:19:19AM +0800, Wang Sheng-Hui wrote: > > > > > > > > > > > > On 6/1/2016 3:40 PM, Minchan Kim wrote: > > > > > On Wed, Jun 01, 2016 at 11:42:29AM +0800, Wang Sheng-Hui wrote: > > > > >> Dear, > > > > >> > > > > >> Sorry to trouble you. > > > > >> > > > > >> I noticed cma_alloc would turn to __alloc_contig_migrate_range for allocating pages. > > > > >> But __alloc_contig_migrate_range calls migrate_prep() at first, even if the requested page > > > > >> is single and free, lru_add_drain_all still run (called by migrate_prep())? > > > > >> > > > > >> Image a large chunk of free contig pages for CMA, various drivers may request a single page from > > > > >> the CMA area, we'll get lru_add_drain_all run for each page. > > > > >> > > > > >> Should we detect if the required pages are free before migrate_prep(), or detect at least for single > > > > >> page allocation? > > > > > That makes sense to me. > > > > > > > > > > How about calling migrate_prep once migrate_pages fails in the first trial? > > > > > > > > Minchan, > > > > > > > > I tried your patch in my env, and the number of calling migrate_prep() dropped a lot. > > > > > > > > In my case, CMA reserved 512MB, and the linux will call migrate_prep() 40~ times during bootup, > > > > most are single page allocation request to CMA. > > > > With your patch, migrate_prep() is not called for the single pages allocation requests as the free > > > > pages in CMA area is enough. > > > > > > > > Will you please push the patch to upstream? > > > > > > It is not correct. > > > > > > migrate_prep() is called to move lru pages in lruvec to LRU. In > > > isolate_migratepages_range(), non LRU pages are just skipped so if > > > page is on the lruvec it will not be isolated and error isn't returned. > > > So, "if (ret) migrate_prep()" will not be called and we can't catch > > > the page in lruvec. > > > > Ah,, true. Thanks for correcting. > > > > Simple fix is to remove migrate_prep in there and retry if test_pages_isolated > > found migration is failed at least once. > > Hmm...much better than before. But, it makes me wonder what his > painpoint is. He want to remove migrate_prep() which calls > lru_add_drain_all() needlessly. But, we already have one in alloc_contig_range(). > So, he will not be happy entirely with following change. It will reduce the numer of drain IPI call so it would be win compared to old. > Moreover, lru_add_drain_all() is there without any validation. It is there > since we need to gather migrated pages in lruvec but I think that it > is sufficient to call lru_add_drain_cpu() and drain_local_pages(), respectively. Maybe, it is heritage of memory hotplugging. :( Should be more optimized. Hope you will look into that. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>